Robin Williams, in the Moment

Feb. 25, 2011— -- Talking with Academy Award-winning actor Robin Williams can feel like a mental workout.

During an interview with ABC News' Bill Weir, the comedic actor's brain seemed to work in spurts as he changed subjects and slipped into various voices or characters. It's this special talent that has earned him an Oscar, several Grammys and soldout shows on his stand-up comedy tours.

In his current -- and first -- foray on Broadway, he plays the central character in "Bengal Tiger at the Baghdad Zoo," for the next 5½ months.

"My character is a Bengal tiger, who starts out in the zoo and eventually gets killed and becomes a ghost," Williams told "Nightline." "Basically, it's like 'Waiting for Godot' in Iraq."

Now residing near San Francisco, Williams, 59, began his career in the 1970s doing stand-up. He draws his stand-up material, he said, from various moments happening around him, from conversations with people to current events, including the upcoming Oscars.

"When you go out on stand-up, you do like at least a month of just starting off with a base and then as you go out, things will appear in the news, things will happen," he said. "It's weird with 'The King's Speech,' after watching the K-k-k-k-king's Speech and thinking if Hitler had an impediment, we wouldn't have had a problem."

Or, Williams said, he'll come up with material from his own life, such as the open-heart surgery he underwent in 2009.

"After surgery you come up with a whole other thing about what life is and the idea of what surgery was," he said. "The idea of heart failure, the idea of, with all these genetic replacements and genetic enhancements ... eventually it will be like, 'Gil, did you take drugs? You just went 100 meters in 3 seconds.' 'I know it's weird isn't it?'"

After falling in love with drama in high school, Williams attended the Julliard School in New York City in 1973 but left in 1976 to move to Los Angeles. It was there that he landed his big break as the alien Mork in the popular TV sitcom "Mork and Mindy," which ran from 1978 to 1982.

Robin Williams Says His Son's Birth Helped Him Kick Cocaine

Almost 30 years after starring in the show and playing numerous other characters since then, Williams said "Mork" is what strangers on the street still shout out to him.

"Oh yeah, 'Diddy, Diddy,' variations of 'nanoo, nanoo,' 'Pork and Sandy,'" he said. "It was TV, and it hit so big, it's still in people's memory banks. ... At first I was like, I've got an Academy Award, but it's just what people remember."

But with that massive amount of fame early in his career came massive indulgence, and Williams developed an addiction to cocaine in the late 1970s. He said the birth of his first son, Zak, in 1983, was what prompted him to kick the drug habit.

"The one thing that cleaned me up from that was having a kid," he said. "That's immediate. I didn't have any rehabs or groups. I just kind of took my mother's advice of vitamins and exercise. You realize, OK, now you have this responsibility, and [I] dealt with it."

Williams remained sober for decades, through the heights of his movie career. He won an Oscar for Best Supporting Actor for his role as a psychologist in "Good Will Hunting" in 1998, and had been nominated for his roles in "Good Morning, Vietnam" (1987), "Dead Poets Society" (1989) and "The Fisher King" (1991).

Since then, Williams starred in dozens of films and went on several stand-up comedy tours, but in 2006, he relapsed and checked into a substance-abuse rehabilitation center in Oregon.

"I was drinking," he said. "I was just, you know, not a full-out train wreck, but let's just say with one wheel in the sand.

"You get to a point where you fall off," he said. "You think no, I can do it now, I'm OK, I can deal with this, and then you realize, no you can't. ... It didn't take very long to go from one drink to full-out abuse."

Williams said his relapse cost him his 19-year marriage to his second wife, Marsha Garces, who filed for divorce in March 2008, citing irreconcilable differences.

But after he was released from rehab and underwent heart surgery, Williams said he became closer with his children, including his 21-year-old daughter, Zelda, who followed in her father's acting footsteps.

Williams: 'Love Doing What You Do'

"She's made a lot of movies," Williams said. "I haven't watched them because its slasher movies, and she gets killed. So I go, that's my daughter, the one being axed."

As for his next projects, Williams said it's all about waiting for the next script to come in.

"I'm waiting right now," he said. "If something came in today that's supposedly really good ... you just want to find something interesting to do at this point."

As he approaches his 60th birthday, Williams reflected on what he would tell his 30-year-old self.

"Don't be running so fast," he said. "Enjoy. Just take it, slow down if you could, because when you're 30, it's like, 'I've got to do everything now!'... And love doing what you do."